Most conventional polymers derived from petroleum resources such as polyethylene terephthalate (PET), nylon, polyolefin and polyvinyl chloride (PVC) resins, have been used for materials for a wide range of applications such as packaging materials. However, these polymers are resistant to biodegradation and related to environmental issues like carbon dioxide gas, which causes the global warming on the waste treatment processes. In addition, there have been wide studies on the use of biomass-based resins including polylactic acid following the depletion of petroleum resources.
However, as polylactic acid derived from plants is lower in mechanical properties and the like than petroleum-based resins, there have been limitations of the fields and applications to which it is applicable. Particularly, attempts have been made to use polylactic acid resins as packaging materials such as packaging films, but they have failed due to the poor flexibility of polylactic acid resins.
In order to overcome the problems of polylactic acid resins, it has been suggested that low-molecular weight flexibilizers or plasticizers be added to polylactic acid resins, or plasticizers produced by addition polymerization of polyether-based or aliphatic polyester-based polyol be applied to the polylactic acid resins.
However, there is little improvement of flexibility in most of the packaging films comprising polylactic acid resins which are produced according to these methods. Furthermore, the packaging films exhibit poor stability as the plasticizers bleed out over time, and have the disadvantages of an increase in haze together with a decrease in low transparency. In most cases of conventional methods, the plasticizer caused a decrease in mechanical properties of the packaging film, and particularly, the polylactic acid resins which can be easily processed by an extrusion and the like with superior mechanical properties have hardly been suggested. In addition, many cases of adding the plasticizer caused a yellowing of polylactic acid resin and deteriorated the external appearance of the packaging film.
Accordingly, there is a continuous demand for a polylactic acid resin film that has improved flexibility and superior external appearance, and exhibits excellent properties including mechanical property, transparency, heat resistance, anti-blocking property, workability of a film, and the like.